This invention relates to a gas cleaning system for metallurgical vessels.
Pneumatic metallurgical vessels are commonly employed for converting pig iron to steel. These vessels generally include an open upper end for receiving a metallic charge and tuyeres or lances for delivering oxygen or an oxygen containing gas to the metallic charge for the oxidation of such impurities as carbon, phosphorous and silicon. As a result of the reactions within the vessel pollutant gases such as carbon monoxide and particulate material may be discharged from the upper end of the vessel.
One type of pneumatic steel conversion apparatus, commonly called Q-BOP, includes an open topped vessel having tuyeres extending through its lower end for injecting oxygen beneath the level of molten metal within the vessel. In addition, a hydrocarbon shielding fluid, such as propane, manufactured gas, natural gas or light oil, is injected in surrounding relation to the oxygen for prolonging the life of the tuyeres and the surrounding vessel refractory. As a result of the reactions within the vessel and the disassociation of the shielding fluid, pollutant gases and particulate material are discharged from the open upper end of the vessel. Another type of metallurgical vessel is the BOF furnace where oxygen is blown from a lance onto the upper surface of the metal bath causing the discharge of gases such as carbon monoxide and a brown iron-containing smoke.
In order to prevent the discharge of such pollutants, Q-BOP and BOF vessels are commonly provided with a smoke hood coupled to a gas cleaning system. Smoke hoods of this type are normally disposed above the upper end of the vessel and may include a skirt which is movable into and out of close proximity with the vessel opening.
When Q-BOP vessels, for example, are tilted away from the smoke hood for sampling and tapping, a gas, normally nitrogen, must be injected through the furnace tuyeres to prevent the backflow of liquid metal. An enclosure is often provided for containing the fumes which normally discharge from the vessel during such periods. In addition, when the vessel is being charged with liquid hot metal or scrap through a door in the enclosure, a secondary gas emission occurs which must also be controlled. One apparatus for collecting such fumes includes a secondary gas collecting hood which opens into the enclosure and is disposed above the access door for creating an indraft so that the secondary fumes do not pass out of the enclosure. Secondary hoods of this type are connected by a selectively operable valve or damper to the same gas cleaning system as the primary hood. In order for the secondary hood system to be effective, the flow rate of air inwardly through the open access door must be relatively high in order to prevent the outflow of gases emanating from the tilted vessel. Other types of pneumatic metallurgical vessels, such as BOF furnaces, Kaldo, Bessemer and Thomas converters, and argon-oxygen vessels also require emission collectors in varying degrees during blowing and non-blowing stages of their respective process cycles.